In vivo uptake of estrone sulfate by rabbit uterus

The capability of rabbit uterus and liver to hydrolyze estrone sulfate (E1S) to estrone (E1) was demonstrated in vitro by superfusion of tissue slices with mixtures of [3H]-E1S and [14C]E1. However, capillary barriers or binding factors may prevent the utilization of the blood-borne estrogen sulfate. To evaluate the extent of uptake of circulating E1S by uterine cells, a mixture of [3H]E1S and [14C]E1 was injected into the abdominal aorta of anesthetized rabbits. Shortly after the injection, samples of blood, uterine tissue, and liver were simultaneously taken. Isotope ratios in E1 isolated from these samples were measured and compared. The 3H to 14C ratios in E1 isolated from the uterus and from plasma were similar. It was concluded from these results that blood-borne E1S was not taken up directly by the uterus, since, otherwise, uterine E1 would be expected to have a higher 3H to 14C ratio than plasma E1. The isotope ratios in hepatic E1 were higher than those in E1 isolated from plasma or uterus, probably as a result of direct uptake of [3H]E1S by the liver.